The invention relates to an implantation pin, a fixation device, an implantation kit and a method for applying an implantation pin to a target structure. In particular, the invention relates to a bone pin which is formed as a sonic pin.
In the prior art several implantation devices for humans or animals are known. The implants at least partly create positive-fit connections to human or animal tissue parts, particularly skeletal parts, wherein the implants help connect tissue parts together, or help connect tissue parts to means supporting or replacing tissue parts, or to other therapeutic auxiliary devices. Further methods for implanting implants into humans or animals are known.
Known implants for creating connections to skeletal parts such as bones include screws, pins, staples, etc., which are used for connecting bones to bones, or bones to artificial, carrying, stabilizing, or supporting parts, or to parts replacing skeletal parts (stabilization or fixation plates, sutures, wires, artificial joint elements, artificial teeth, bone grafts, etc.). Such connection elements for implantation consist for example of metal or plastic, including resorbable plastic. After healing, the connection elements may be removed by a further operation or they may be left in the body where they are possibly gradually decomposed and replaced by vital tissue.
For stabilizing a bone fracture, a fixation plate with suitable holes may be fixed in the region of the fracture using screws as mentioned above. Plate and screws may consist of metal (e.g. stainless steel or titanium). The screws may be self-cutting and are rotated into threadless openings in the bone, or they may be screwed into pre-drilled threaded openings. Pins may be pushed into previously created openings for similar purposes. Connections created in the foregoing manner are usually based on frictional engagement, possibly on positive fit. Substantial pressure may be applied to living tissue during the implantation.
It is known also to use curable, plastic materials (e.g. particular cements on a water or polymer base) for creating connections of the mentioned type. Such materials are pressed from the outside between implant and vital tissue, or into tissue defects in a highly viscous condition, and are cured in situ. Positive-fit connections can be created using such material, if the openings into which the material is pressed comprise suitable undercuts. In order to reduce the stress and/or costs of the corresponding operation method so-called biodegradable implants, e.g. bone pins, may be used. That is, bone pins which degrade over time and which are then absorbed by the body. One of such known biodegradable bone pins is known under the trademark Polypin. This bone pin consists of a polyactid-copolymer mixture and is absorbed during a period of about two years.
Also known in the art is the usage of thermoplastic polymer materials which can be liquefied in a targeted manner by way of mechanical oscillation such as ultrasonic oscillations and, in this condition, can be pressed into cavities by way of hydrostatic pressure, thereby creating positive fit connections after solidification.
Such implants may serve for creating positive-fit connections to tissue parts and may consist at least partly of a material that can be liquefied at a relatively low temperature (<250° C.) by way of mechanical oscillation energy such that the material can be pressed into pores or other openings of the tissue part by the effect of external pressure to form positive-fit connections when re-solidified.
In a prior art approach an implantation pin for implantation in a target structure comprises a base region and a shaft region. The base region comprises a connection portion which is adapted to interact with a coupling region of a sonotrode applying ultrasonic vibrations. The shaft region comprises a material which can be liquefied by applying ultrasonic vibrations. Accordingly, when ultrasonic vibrations are generated within the sonotrode and transmitted to the base region of the implantation pin, these ultrasonic vibrations are further transmitted to the shaft region. At a surface, where the shaft region abuts to the target structure, such as for example a bone into which a recess has been formed in order to accommodate the implantation pin, the local surface temperature increases due to friction between the target structure and the vibrated implantation pin. This surface temperature increase causes a melting of the liquefiable material such that the latter can then flow into pores of the bone. After re-solidifying of the liquefiable material a positive-fit connection between the implantation pin and the bone may be created.
However, with this prior art implantation pin, the surfaces of the shaft region of the implantation pin which are to be connected to the target structure have to be in direct contact to the target structure while applying the ultrasonic vibrations. For example, when the implantation pin is to be fixed within a bone, it has to be inserted into a previously prepared recess within the bone and has to contact the inside surface walls of the recess in order to liquefy the shaft region material at these locations. For this purpose, it might be necessary to precisely adapt the geometry of the implantation pin to the geometry of the recess in the bone. Furthermore, it might be necessary to exert substantial pressure to the implantation pin while applying the ultrasonic vibrations in order to liquefy the shaft region material and this substantial pressure might be transmitted to the inside surface of the recess at which location the bone might be sensible for damages.
Furthermore, the above prior art implantation pin must have sufficient rigidity in order to transmit the ultrasonic vibrations applied to the base region to the shaft region such that the shaft region is sufficiently vibrated in order to melt the liquefiable material at this shaft location.
Ultrasonic bone implants are disclosed in U.S. Pat. No. 6,921,264 and U.S. Publication No. 2006/0105295 the disclosures of which are incorporated herein by reference.